It is possible to detect small discontinuities in a flow. Apparatus for such detection is fully set forth in Abts U.S. Pat. No. 4,112,773, Abts U.S. Pat. No. 4,214,484, and Abts U.S. Pat. No. 4,217,781, all hereby incorporated by reference.
In addition, it may also be desirable to identify the type of discontinuity. It is known that ultrasonic reflections from large solid objects have some different characteristics.